We present a general object-oriented approach to the lexical encoding of multi-word expressions (MWEs) that is couched into the framework of eXtensible MetaGrammar (XMG). We think that XMG provides the flexibility and power needed to account for both regular and idiosyn-cratic aspects of MWEs, which enables the lexicographer to encode MWEs in a transparent and yet factorized way. We compare XMG with two other existing formats for lexical encoding of MWEs, DuELME and Walenty, which have been coupled with real-size grammars and provide mechanisms to avoid description redundancy. We claim that XMG offers additional facilities that reinforce the virtues of its competitors. In this work we confine ourselves to syntax and morphology.